According to the U.S. Center for Disease Control and Prevention, nosocomial bloodstream infections are a leading cause of death in the United States. Approximately five percent of the seven million central venous catheters (CVCs) inserted annually in the United States are associated with at least one episode of bloodstream infection (approximately 350,000 a year). Catheter-related bloodstream infections occur when bacteria enter the bloodstream through an intravenous catheter and can be life threatening.
Skin and soft tissue infections (SSTIs) (also known as complicated and/or uncomplicated skin and skin structure infections (SSSIs)) are a common medical condition and often the consequence of trauma or surgical procedures. Staphylococcus aureus and Streptococcus pyogenes are the pathogens most frequently isolated from patients with deep tissue infections, although any pathogenic organism, including those found on healthy skin, may cause infection. Many SSTIs are mild to moderate in severity, permitting successful treatment with oral antimicrobial agents and local cleansing. In contrast, more severe or complicated infections, which frequently occur in patients with underlying risk factors (e.g., vascular compromise, diabetes) and/or infections caused by difficult-to-treat or multiply-resistant bacteria, may require potent intravenous antimicrobial therapy and aggressive surgical debridement.
Staphylococci are a clinical and therapeutic problem and have been increasingly associated with nosocomial infections since the early 1960s. The coagulase-positive species methicillin-resistant Staphylococcus aureus (MRSA) has long been problematic in both community-acquired and nosocomial infections, and several coagulase-negative staphylococci have been recognized as opportunistic human pathogens, especially in the treatment of critically ill patients in intensive care units. Another major cause for clinical concern is the increasing isolation of penicillin-resistant Streptococcus pneumoniae strains in many parts of the world.
The glycopeptide antibiotics vancomycin and teicoplanin have been used against serious nosocomial infections caused by multi-drug-resistant Gram-positive pathogens, particularly MRSA, coagulase-negative staphylococci (CoNS), and enterococci. Vancomycin and teicoplanin are used for infections caused by MRSA, and until recently, all isolates were uniformly susceptible. However, the isolation of Staphylococcus aureus strains with intermediate susceptibility or resistance to teicoplanin as well as vancomycin has now been reported with increasing frequency. A number of vancomycin-resistant strains, classified “VanA,” “VanB,” or “VanC,” based on the mechanism of resistance, have been reported. Thus, alternative treatment options are needed.
Teicoplanin is at least as active as vancomycin against most Gram-positive bacteria and appears to cause fewer adverse events. Both forms of treatment require at least once daily dosing to effect complete recovery. Currently, the therapeutic options for severe infections caused by some of these pathogens are quite limited. The emerging resistance of Gram-positive pathogens to vancomycin makes the availability of new antibiotics with potential for increased effectiveness highly desirable.
In addition, less frequent dosing regimens than currently-available therapies would be desirable to enhance patient comfort, especially for parenteral, e.g., intravenous or intramuscular, antibiotic administration. Hospital stays are sometimes necessitated by the need for multi-daily antibiotic administration by parenteral means, and less frequent dosing would be advantageous to permit such treatment to be done on an outpatient basis.
Although less frequent dosing is a desirable feature of an antibiotic administration regimen, the “pharmaceutical window,” i.e., the toxicity profile, of the administered antibiotic must be sufficiently acceptable to permit a large single dose to be administered without jeopardizing treatment by causing severe adverse reactions in the treated patient. Further, even when an antibiotic exhibits a suitable pharmaceutical window, less frequent dosing is possible only if the antibiotic exhibits a suitable serum half-life to maintain therapeutic effectiveness over the dosing interval desired. The serum half-life of an antibiotic dictates both the longevity of a drug in vivo and the length of time after administration when the serum level will reach a minimum trough level which is still bactericidally effective. The serum trough level over time after administration of a first dose of antibiotic dictates when a further dose must be administered to retain a minimum bactericidal level of the antibiotic in vivo.
Recently, successful glycopeptide antibiotics have been rationally synthesized from natural glycopeptides. For example, the semisynthetic glycopeptide dalbavancin was synthesized from the natural antibiotic A 40926, originally isolated from an Actinomadura culture (Malabarba et al., 1998, U.S. Pat. No. 5,750,509). Dalbavancin has shown greater efficacy against various bacterial strains than vancomycin or the antibiotic linezolid and represents a promising new treatment for skin and soft tissue infections (see, e.g., Jabés et al., 2004, Antimicrob. Agents Chemother. 48:1118-1123). According to U.S. Pat. No. 5,750,509, dalbavancin is a glycopeptide antibiotic with a monomethyl moiety at its N15 amino (see FIG. 1 for numbering), and this N15-monomethyl amino could be free (i.e. —NHCH3) or protected with an amino protecting group such as t-butoxycarbonyl, carbobenzyloxy, arylalkyl or benzyl. The method for making certain of the dalbavancin components reported in the '509 patent also produced N15,N15-dialkyl analogs of dalbavancin in minor-quantities, but these molecules were not characterized.
In view of the above pathogens, further antibiotics possessing activity against one or more microbes, including antibiotic resistant bacteria, would be of commercial value and would satisfy a long-felt need in the art.